During drilling operations in oil or gas deposits, crossing permeable or fractured regions can cause a partial or even total loss of drilling mud.
For reasons of economy (cost of drilling mud) and of safety (stability of the work), it is absolutely necessary to carry out prompt plugging of the circulation losses. It is known in the art to resort to grouts of hydrosoluble monomers (for example, acrylamide, methylolacrylamide, and other acrylic and methacrylic derivatives) which, when suitably formulated (such as by addition of catalysts, weighting materials, viscosity modifiers, and/or retardants), polymerize to a (hydro)gel of three-dimensional structure which is insoluble in water but is capable of swelling when in contact with water.
These grouts are satisfactorily employed for drilling operations at depths at which the temperature is from 0.degree. to 60.degree. C.; however, the use of these grouts at greater depths generally does not work for more than 10 hours because the temperature rise, which is a function of the depth, causes a substantial shortening of the setting time.
It is also known in the art to stabilize vinyl monomers using N-nitrosophenylhydroxylamine salts as taught in U.S. Pat. Nos. 2,758,131 and 2,773,874, and German patent No. 1,239,679. However, such inhibitors are not sufficiently effective at elevated temperatures, especially above 80.degree. C.